1. Technical Field
The present invention relates to an angular velocity sensor.
2. Description of the Related Art
Recently, an angular velocity sensor has been used in various fields, for example, the military, such as an artificial satellite, a missile, an unmanned aircraft, or the like, vehicles, such as an air bag, electronic stability control (ESC), a black box for a vehicle, or the like, hand shaking prevention of a camcorder, motion sensing of a mobile phone or a game machine, navigation, or the like.
The angular velocity sensor generally adopts a configuration in which a mass body is bonded to a flexible substrate such as a membrane, or the like, so as to measure acceleration and angular velocity. Through the configuration, the angular velocity sensor may calculate the angular velocity by measuring Coriolis force applied to the mass body.
A process of measuring the acceleration and the angular velocity by using the angular velocity sensor will be described in detail below. First, the angular velocity may be obtained by Coriolis force “F=2mΩ·v”, where “F” represents the Coriolis force applied to the mass body, “m” represents the mass of the mass body, “Ω” represents the angular velocity to be measured, and “v” represents the motion velocity of the mass body. Among others, since the motion velocity v of the mass body and the mass m of the mass body are values that are known in advance, the angular velocity Ω may be obtained by sensing the Coriolis force (F) applied to the mass body.
Meanwhile, the angular velocity sensor according to the prior art includes a piezoelectric material formed over a membrane (diaphragm) so as to drive the mass body or sense a displacement of the mass body, as described in a patent document of the following prior art document. In order to measure angular velocity with the angular velocity sensor, it is preferable to substantially coincide a resonance frequency of a driving mode to a resonance frequency of a sensing mode. However, very large interference occurs between the driving mode and the sensing mode due to fine manufacturing errors caused by shape/stress/physical properties, and the like. Therefore, noise signals much larger than the angular signal are output and then, circuit amplification of the angular signal is limited, thereby degrading sensitivity of the angular velocity sensor.